1. Field of the Invention
The present invention relates to a scanner lens for reading which can be used in a scanner for a facsimile, a digital copying machine, a computer or a word processor.
2. Description of the Related Art
Recently, a novel image sensor such as a three-line one-chip charge coupled device (CCD) has been developed to read a color image. In this image sensor, for example, a light receiving element having red, green and blue filters is arranged on three lines on one chip. A color original image is focused and formed on a light receiving face of the light receiving element. Thus, the original image can be changed to an electric signal by decomposing the original image into three primary colors. It is desirable to preferably apply the scanner lens for reading to such an image sensor.
To preferably read a color original by the above image sensor, it is necessary to preferably perform achromatic processing of the scanner lens with respect to each of red, green and blue such that forming positions of the red, green and blue color images are in conformity with each other on the light receiving face of the image sensor. With respect to the image sensor, it is necessary to correct achromatism of the scanner lens with very high accuracy to generally focus and form a reduced image of the original in size.
There is generally no known scanner lens for reading processed with respect to achromatism such that the scanner lens can be preferably applied to an image sensor such as the above three-line one-chip charge coupled device (CCD).
Further, it is necessary to read a large-sized original at a high speed in a recent image sensor. To satisfy such a requirement, it is desirable to set the scanner lens for reading to have a wide field angle and a large aperture.